Staff in the store helped to detain a suspect – a 36-year-old man from Leeds – who was last night being quizzed by detectives.

Liam Hughes, a Big Issue seller, described the incident as “absolute madness”.

PIC: Tony Johnson

He said: “I started wondering what was going on. But then I’ve seen this fellow come out with the ambulance crew and he gets put in the ambulance.

“I saw then, about five or 10 minutes later, I’ve seen one of the police officers come out with one of those plastic tubes with a penknife in it and I sort of put two and two together and thought ‘someone’s been stabbed here’.”

The officer was taken by ambulance to hospital, where he received stitches for his injuries before being released.

Mr Smart said: “This could quite easily have ended up with the death of officer given where the injures were inflicted.

“He’s a lucky lad, but he’s got the physical injuries and people underestimate the mental side of being assaulted.”

He said support such as that shown by YEP readers, who praised the officer’s bravery and sent best wishes via our Facebook page, made “it all worthwhile” for officers.

The store was closed following the attack just after 9am to allow crime scene investigators to carry out forensic work.

It had reopened by lunchtime, meaning the album signing was able to go ahead.

Contact Leeds District CID via 101, quoting 344 of November 25, with information.